The Clinical Syndrome of Paroxysmal Exercise-Induced Dystonia: Diagnostic Outcomes and an Algorithm

Misdiagnosis of functional neurological symptom disorders in paediatrics: Narrative review and relevant case report

Functional neurological symptom disorders (FNSD) pose a common challenge in clinical practice, particularly in pediatric cases where the clinical phenotypes can be intricate and easily confused with structural disturbances. The frequent coexistence of FNSDs with other medical disorders often results in misdiagnosis. In this review, we highlight the distinctions between FNSD and various psychiatric and neurological conditions. Contrary to the misconception that FNSD is a diagnosis of exclusion, we underscore its nature as a diagnosis of inclusion, contingent upon recognizing specific clinical features. However, our focus is on a critical learning point illustrated by the case of a 14-year-old male initially diagnosed with FNSD, but subsequently found to have a rare primary monogenic movement disorder (paroxysmal kinesigenic dyskinesia, PKD). The crucial takeaway from this case is the importance of avoiding an FNSD diagnosis based solely on psychiatric comorbidity and suppressible symptoms. Instead, clinicians should diligently assess for specific features indicative of FNSD, which were absent in this case. This emphasizes the importance of making a diagnosis of inclusion. Extended follow-up and clinical-oriented genetic testing might help identify comorbidities, prevent misdiagnosis, and guide interventions in complex cases, which cannot be simply classified as "functional" solely because other conditions can be excluded.

Pearls & Oy-sters: Paroxysmal Exercise-Induced Dyskinesias Due to Pyruvate Dehydrogenase Deficiency

Paroxysmal exercise-induced movement disorders may be caused by energy metabolism disorders, such as Glut 1 deficiency, pyruvate dehydrogenase deficiency, or mitochondrial respiratory chain disorders. A 4-year-old boy with a history of febrile seizures presented with paroxysmal dystonia, triggered by exercise, or occurring at rest. Additional investigations demonstrated pallidal hyperintensities on brain MRI and low CSF glucose. Pyruvate and lactate were elevated. The clinical presentation combined with neuroimaging abnormalities and biochemical profile (the lactate/pyruvate ratio) were clues to pyruvate dehydrogenase deficiency, a treatable metabolic disorder with neurologic presentations.

Parkinson's Disease, Parkinsonisms, and Mitochondria: the Role of Nuclear and Mitochondrial DNA

PURPOSE OF REVIEW

Overwhelming evidence indicates that mitochondrial dysfunction is a central factor in Parkinson's disease (PD) pathophysiology. This paper aims to review the latest literature published, focusing on genetic defects and expression alterations affecting mitochondria-associated genes, in support of their key role in PD pathogenesis.

RECENT FINDINGS

Thanks to the use of new omics approaches, a growing number of studies are discovering alterations affecting genes with mitochondrial functions in patients with PD and parkinsonisms. These genetic alterations include pathogenic single-nucleotide variants, polymorphisms acting as risk factors, and transcriptome modifications, affecting both nuclear and mitochondrial genes. We will focus on alterations of mitochondria-associated genes described by studies conducted on patients or on animal/cellular models of PD or parkinsonisms. We will comment how these findings can be taken into consideration for improving the diagnostic procedures or for deepening our knowledge on the role of mitochondrial dysfunctions in PD.

Paroxysmal movement disorders: Paroxysmal dyskinesia and episodic ataxia

Paroxysmal movement disorders have traditionally been classified into paroxysmal dyskinesia (PxD), which consists in attacks of involuntary movements (mainly dystonia and/or chorea) without loss of consciousness, and episodic ataxia (EA), which features spells of cerebellar dysfunction with or without interictal neurological manifestations. In this chapter, PxD will be discussed first according to the trigger-based classification, thus reviewing clinical, genetic, and molecular features of paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia, and paroxysmal exercise-induced dyskinesia. EA will be presented thereafter according to their designated gene or genetic locus. Clinicogenetic similarities among paroxysmal movement disorders have progressively emerged, which are herein highlighted along with growing evidence that their pathomechanisms overlap those of epilepsy and migraine. Advances in our comprehension of the biological pathways underlying paroxysmal movement disorders, which involve ion channels as well as proteins associated with the vesical synaptic cycle or implicated in neuronal energy metabolism, may represent the cornerstone for defining a shared pathophysiologic framework and developing target-specific therapies.

Paroxysmal exercise-induced dyskinesia without involuntary movements

A 66-year-old British man was referred to our department because of a 2.5 year history of bilateral paroxysmal weakness of the lower limbs. It occurred when he walked for about 10 minutes, so he would stop in place and spontaneously rest for up to 15 minutes. When carbamazepine 200 mg/day was administered, the severity and frequency of the symptoms reduced by half and resolved when the dose was increased to 300 mg/day. Even if no involuntary movement is observed, paroxysmal exercise-induced dyskinesia should be considered in patients with paroxysmal painless gait disturbance, and a therapeutic trial of anticonvulsants may be helpful.

The effect of body weight-supported overground gait training for patients with Parkinson's disease: A retrospective case-control observational study

Objective

To evaluate the effects of body weight-supported overground gait training (BWSOGT) on motor abilities, such as gait and balance, in patients with Parkinson’s disease (PD).

Design

Retrospective case-controlled observational study with a 4-week follow-up.

Setting

Inpatient rehabilitation.

Participants

We selected 37 of 68 patients with PD. Inclusion criteria were (1) Hoehn & Yahr stage II–IV, (2) no medication adjustment during the study period, (3) at least 1 week since last medication adjustment, and (4) ability to walk more than 10 meters on their own. Exclusion criteria were (1) cerebrovascular disease or other complications affecting movement, (2) difficulty in measurement, (3) early discharge, (4) medication change during the study, and (5) development of complications.

Interventions

Patients were divided into two groups. Patients in Group I underwent 20 minutes of BWSOGT with a mobile hoist in addition to the standard exercises; Group II performed 20 minutes of gait training in place of BWSOGT. In both groups, training was performed for a total of 15 times/4 weeks.

Main outcome measure(s)

Participants were evaluated using the Unified Parkinson’s Disease Rating Scale total, part II, and part III; 10-m walk test; velocity; stride length; 6-minute walk test; timed up and go test; Berg Balance Scale; and freezing of gait before and after the intervention.

Results

There were significant decreases in the Unified Parkinson’s Disease Rating Scale total, part II, and part III in both groups; however, 6-minute walk test, timed up and go test, and freezing of gait results only improved in Group I.

Conclusions

BWSOGT for patients with PD improves gait ability and dynamic balance more than standard gait training.

Genetics of Paroxysmal Dyskinesia: Novel Variants Corroborate the Role of KCNA1 in Paroxysmal Dyskinesia and Highlight the Diverse Phenotypic Spectrum of KCNA1- and SLC2A1-Related Disorders

Paroxysmal dyskinesias (PxD) are rare movement disorders with characteristic episodes of involuntary mixed hyperkinetic movements. Scientific efforts and technical advances in molecular genetics have led to the discovery of a variety of genes associated with PxD; however, clinical and genetic information of rarely affected genes or infrequent variants is often limited. In our case series, we present two individuals with PxD including one with classical paroxysmal kinesigenic dyskinesia, who carry new likely pathogenic de novo variants in KCNA1 (p.Gly396Val and p.Gly396Arg). The gene has only recently been discovered to be causative for familial paroxysmal kinesigenic dyskinesia. We also provide genetic evidence for pathogenicity of two newly identified disease-causing variants in SLC2A1 (p.Met96Thr and p.Leu231Pro) leading to paroxysmal exercise-induced dyskinesia. Since clinical information of carriers of variants in known disease-causing genes is often scarce, we encourage to share clinical data of individuals with rare or novel (likely) pathogenic variants to improve disease understanding.

Pediatric Paroxysmal Exercise-Induced Neurological Symptoms: Clinical Spectrum and Diagnostic Algorithm

Paroxysmal exercise-induced neurological symptoms (PENS) encompass a wide spectrum of clinical phenomena commonly presenting during childhood and characteristically elicited by physical exercise. Interestingly, few shared pathogenetic mechanisms have been identified beyond the well-known entity of paroxysmal exercise-induced dyskinesia, PENS could be part of more complex phenotypes including neuromuscular, neurodegenerative, and neurometabolic disease, epilepsies, and psychogenetic disorders. The wide and partially overlapping phenotypes and the genetic heterogeneity make the differential diagnosis frequently difficult and delayed; however, since some of these disorders may be treatable, a prompt diagnosis is mandatory. Therefore, an accurate characterization of these symptoms is pivotal for orienting more targeted biochemical, radiological, neurophysiological, and genetic investigations and finally treatment. In this article, we review the clinical, genetic, pathophysiologic, and therapeutic landscape of paroxysmal exercise induced neurological symptoms, focusing on phenomenology and differential diagnosis.

Genetic updates on paroxysmal dyskinesias

The paroxysmal dyskinesias are a diverse group of genetic disorders that manifest as episodic movements, with specific triggers, attack frequency, and duration. With recent advances in genetic sequencing, the number of genetic variants associated with paroxysmal dyskinesia has dramatically increased, and it is now evident that there is significant genotype-phenotype overlap, reduced (or incomplete) penetrance, and phenotypic variability. In addition, a variety of genetic conditions can present with paroxysmal dyskinesia as the initial symptom. This review will cover the 34 genes implicated to date and propose a diagnostic workflow featuring judicious use of whole-exome or -genome sequencing. The goal of this review is to provide a common understanding of paroxysmal dyskinesias so basic scientists, geneticists, and clinicians can collaborate effectively to provide diagnoses and treatments for patients.

The Spectrum of PRRT2-Associated Disorders: Update on Clinical Features and Pathophysiology

Mutations in the PRRT2 (proline-rich transmembrane protein 2) gene have been identified as the main cause of an expanding spectrum of disorders, including paroxysmal kinesigenic dyskinesia and benign familial infantile epilepsy, which places this gene at the border between epilepsy and movement disorders. The clinical spectrum has largely expanded to include episodic ataxia, hemiplegic migraine, and complex neurodevelopmental disorders in cases with biallelic mutations. Prior to the discovery of PRRT2 as the causative gene for this spectrum of disorders, the sensitivity of paroxysmal kinesigenic dyskinesia to anticonvulsant drugs regulating ion channel function as well as the co-occurrence of epilepsy in some patients or families fostered the hypothesis this could represent a channelopathy. However, recent evidence implicates PRRT2 in synapse functioning, which disproves the "channel hypothesis" (although PRRT2 modulates ion channels at the presynaptic level), and justifies the classification of these conditions as synaptopathies, an emerging rubric of brain disorders. This review aims to provide an update of the clinical and pathophysiologic features of PRRT2-associated disorders.

Levetiracetam-responsive paroxysmal exertional dyskinesia in a Welsh Terrier

A 5-and-a-half-year old, 9-kg, spayed, female Welsh Terrier presented with a 12 month history of paroxysmal exertion-induced dyskinesia (PED) characterized by recurrent episodes of involuntary hyperkinetic movements, abnormal muscle tone, and contractions triggered by exercise. A single episode occurred within 2 hours after exercise, lasted from 7 to 10 minutes, and resolved without treatment. The owner sought treatment for the dog when the episodes began to last longer (20-30 minutes), and occurred as long as 2.5 to 8 hours after exercise. Diazepam administered intranasally at the start of an episode promptly alleviated the symptoms. Maintenance therapy with levetiracetam proved effective, such that the dog was gradually returned to exercise. However, attempts to wean the dog off the drug resulted in reoccurrence. Although the pathophysiology of PED is not fully understood, the clinical presentation and the positive response to antiepileptic therapy highlight the overlap between disease pathways in epilepsy and PED in dogs.

Movement Disorders and Hematologic Diseases

BACKGROUND

Movement disorders can be associated with or caused by hematological abnormalities. The objective of this review is to highlight features that will aid in the clinician's recognition and treatment of these disorders.

METHODS

MESH terms relevant to movement disorders and hematologic diseases were searched to identify conditions included in this narrative, educational review.

RESULTS

Several conditions were identified, and they were organized by hematologic categories to include red blood cell abnormalities, white blood cell abnormalities, disorders of clotting and bleeding, hematologic malignancies, and others.

CONCLUSIONS

This review will increase providers' understanding of disorders that include movement disorders and hematologic abnormalities. Basic hematologic laboratories can aid in assessment of these disorders, to include complete blood count/hemogram and peripheral blood smear. Recognition is key, especially in the setting of underlying malignancy, vitamin deficiency, or other disorder in which treatment is available.

The Phenotypic Variation of a Parkin-Related Parkinson's Disease Family and the Role of Heterozygosity

Background

Parkinson's disease (PD) is a common neurodegenerative disorder with both sporadic occurrence and Mendelian heredity, as it is true for autosomal recessive parkin-related PD (PARK-parkin). Parkin-related PD is characterized by early onset, slow progression, frequent lower limb dystonia, and a robust response to levodopa. Clinicians are increasingly confronted with heterozygous PD patients mimicking dominant inheritance. Nevertheless, the exact clinical implications of heterozygosity are not fully understood.

Cases

We present an illustrative PARK-parkin family with 2 affected sisters (compound heterozygous) and their father (heterozygous). One sister expresses the classical phenotype, whereas the other has isolated jerky tremor. The father has left-sided action tremor of the hand with some dystonic posturing without clear bradykinesia and normal DaTSCAN.

Conclusion

This case series illustrates the phenotypic variability in parkin-related PD with 1 classical phenotype and 1 patient with isolated jerky tremor. Unilateral hand tremor of the heterozygous father could mislead genetic testing by mimicking dominant inheritance.

Paroxysmal movement disorders - practical update on diagnosis and management

Introduction: Paroxysmal dyskinesias and episodic ataxias are often caused by mutations in genes related to cell membrane and synaptic function. Despite the exponential increase in publications of genetically confirmed cases, management remains largely clinical based on non-systematic evidence. Areas covered: The authors provide a historical and clinical review of the main types of paroxysmal dyskinesias and episodic ataxias, with recommendations for diagnosis and management of patients suffering from these conditions. Expert opinion: After secondary paroxysmal dyskinesias, the most common paroxysmal movement disorders are likely to be PRRT2-associated paroxysmal kinesigenic dyskinesias, which respond well to small doses of carbamazepine, and episodic ataxia type 2, which often responds to acetazolamide. Familial paroxysmal non-kinesigenic dyskinesias are largely caused by mutations in PNKD and have poor response to therapy but improve with age. Exercise-induced dyskinesias are genetically heterogeneous, caused by disorders of glucose transport, mitochondrial function, dopaminergic pathways or neurodegenerative conditions amongst others. GNAO1 and ADCY5 mutations can also cause paroxysmal movement disorders, often in the context of ongoing motor symptoms. Although a therapeutic trial is justified for classic cases and in limited resource settings, genetic testing may help direct initial or rescue therapy. Deep brain stimulation may be an option for severe cases.

The spectrum of paroxysmal dyskinesias

Paroxysmal dyskinesias (PxD) comprise a group of heterogeneous syndromes characterized by recurrent attacks of mainly dystonia and/or chorea, without loss of consciousness. PxD have been classified according to their triggers and duration as paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia and paroxysmal exertion-induced dyskinesia. Of note, the spectrum of genetic and nongenetic conditions underlying PxD is continuously increasing, but not always a phenotype–etiology correlation exists. This creates a challenge in the diagnostic work-up, increased by the fact that most of these episodes are unwitnessed. Furthermore, other paroxysmal disorders, included those of psychogenic origin, should be considered in the differential diagnosis. In this review, some key points for the diagnosis are provided, as well as the appropriate treatment and future approaches discussed.

Dystonia and Parkinson's disease: What is the relationship?

Dystonia and Parkinson's disease are closely linked disorders sharing many pathophysiological overlaps. Dystonia can be seen in 30% or more of the patients suffering with PD and sometimes can precede the overt parkinsonism. The response of early dystonia to the introduction of dopamine replacement therapy (levodopa, dopamine agonists) is variable; dystonia commonly occurs in PD patients following levodopa initiation. Similarly, parkinsonism is commonly seen in patients with mutations in various DYT genes including those involved in the dopamine synthesis pathway. Pharmacological blockade of dopamine receptors can cause both tardive dystonia and parkinsonism and these movement disorders syndromes can occur in many other neurodegenerative, genetic, toxic and metabolic diseases. Pallidotomy in the past and currently deep brain stimulation largely involving the GPi are effective treatment options for both dystonia and parkinsonism. However, the physiological mechanisms underlying the response of these two different movement disorder syndromes are poorly understood. Interestingly, DBS for PD can cause dystonia such as blepharospasm and bilateral pallidal DBS for dystonia can result in features of parkinsonism. Advances in our understanding of these responses may provide better explanations for the relationship between dystonia and Parkinson's disease.

Current therapies and therapeutic decision making for childhood-onset movement disorders

Movement disorders differ in children to adults. First, neurodevelopmental movement disorders such as tics and stereotypies are more prevalent than parkinsonism, and second, there is a genomic revolution which is now explaining many early-onset dystonic syndromes. We outline an approach to children with movement disorders starting with defining the movement phenomenology, determining the level of functional impairment due to abnormal movements, and screening for comorbid psychiatric conditions and cognitive impairments which often contribute more to disability than the movements themselves. The rapid improvement in our understanding of the etiology of movement disorders has resulted in an increasing focus on precision medicine, targeting treatable conditions and defining modifiable disease processes. We profile some of the key disease-modifying therapies in metabolic, neurotransmitter, inflammatory, and autoimmune conditions and the increasing focus on gene or cellular therapies. When no disease-modifying therapies are possible, symptomatic therapies are often all that is available. These classically target dopaminergic, cholinergic, alpha-adrenergic, or GABAergic neurochemistry. Increasing interest in neuromodulation has highlighted that some clinical syndromes respond better to DBS, and further highlights the importance of "disease-specific" therapies with a future focus on individualized therapies according to the genomic findings or disease pathways that are disrupted. We summarize some pragmatic applications of symptomatic therapies, neuromodulation techniques, and some rehabilitative interventions and provide a contemporary overview of treatment in childhood-onset movement disorders. © 2019 International Parkinson and Movement Disorder Society.

Unravelling of the paroxysmal dyskinesias

Paroxysmal dyskinesias (PxD) refer to a rare group of clinically and genetically heterogeneous disorders presenting with recurrent attacks of abnormal movements, typically dystonia, chorea or a combination thereof, without loss of consciousness. Classically, PxD have been categorised according to their triggers and duration of the attacks, but increasing evidence suggests that there is a certain degree of clinical and genetic overlap and challenges the concept that one phenotype is attributable to one single aetiology. Here we review the increasing spectrum of genetic conditions, as well as of other non-genetic disorders, that might present with PxD, provide criteria for case definition and propose a diagnostic workup to reach a definitive diagnosis, on which treatment is heavily dependent.

Dystonia

Dystonia is a neurological condition characterized by abnormal involuntary movements or postures owing to sustained or intermittent muscle contractions. Dystonia can be the manifesting neurological sign of many disorders, either in isolation (isolated dystonia) or with additional signs (combined dystonia). The main focus of this Primer is forms of isolated dystonia of idiopathic or genetic aetiology. These disorders differ in manifestations and severity but can affect all age groups and lead to substantial disability and impaired quality of life. The discovery of genes underlying the mendelian forms of isolated or combined dystonia has led to a better understanding of its pathophysiology. In some of the most common genetic dystonias, such as those caused by TOR1A, THAP1, GCH1 and KMT2B mutations, and idiopathic dystonia, these mechanisms include abnormalities in transcriptional regulation, striatal dopaminergic signalling and synaptic plasticity and a loss of inhibition at neuronal circuits. The diagnosis of dystonia is largely based on clinical signs, and the diagnosis and aetiological definition of this disorder remain a challenge. Effective symptomatic treatments with pharmacological therapy (anticholinergics), intramuscular botulinum toxin injection and deep brain stimulation are available; however, future research will hopefully lead to reliable biomarkers, better treatments and cure of this disorder.

The epileptic and nonepileptic spectrum of paroxysmal dyskinesias: Channelopathies, synaptopathies, and transportopathies

Historically, the syndrome of primary paroxysmal dyskinesias was considered a group of disorders as a result of ion channel dysfunction. This proposition was primarily based on the discovery of mutations in ion channels, which caused other episodic neurological disorders such as epilepsy and migraine and also supported by the frequent association between paroxysmal dyskinesias and epilepsy. However, the discovery of the genes responsible for the 3 classic forms of paroxysmal dyskinesias disproved this ion channel theory. On the other hand, novel gene mutations implicating ion channels have been recently reported to produce episodic movement disorders clinically similar to the classic paroxysmal dyskinesias. Here, we review the clinical and pathophysiological aspects of the paroxysmal dyskinesias, further proposing a pathophysiological framework according to which they can be classified as synaptopathies (proline-rich transmembrane protein 2 and myofibrillogenesis regulator gene), channelopathies (calcium-activated potassium channel subunit alpha-1 and voltage-gated sodium channel type 8), or transportopathies (solute carrier family 2 member 1). This proposal might serve to explain similarities and differences among the various paroxysmal dyskinesias in terms of clinical features, treatment response, and natural history. © 2017 International Parkinson and Movement Disorder Society.

Paroxysmal exercise-induced dystonia within the phenotypic spectrum of ECHS1 deficiency

BACKGROUND

ECHS1 encodes a mitochondrial enzyme involved in the degradation of essential amino acids and fatty acids. Recently, ECHS1 mutations were shown to cause a new severe metabolic disorder presenting as Leigh or Leigh-like syndromes. The objective of this study was to describe a family with 2 siblings affected by different dystonic disorders as a resulting phenotype of ECHS1 mutations.

METHODS

Clinical evaluation, MRI imaging, genome-wide linkage, exome sequencing, urine metabolite profiling, and protein expression studies were performed.

RESULTS

The first sibling is 17 years old and presents with generalized dystonia and severe bilateral pallidal MRI lesions after 1 episode of infantile subacute metabolic encephalopathy (Leigh-like syndrome). In contrast, the younger sibling (15 years old) only suffers from paroxysmal exercise-induced dystonia and has very mild pallidal MRI abnormalities. Both patients carry compound heterozygous ECHS1 mutations: c.232G>T (predicted protein effect: p.Glu78Ter) and c.518C>T (p.Ala173Val). Linkage analysis, exome sequencing, cosegregation, expression studies, and metabolite profiling support the pathogenicity of these mutations. Expression studies in patients' fibroblasts showed mitochondrial localization and severely reduced levels of ECHS1 protein. Increased urinary S-(2-carboxypropyl)cysteine and N-acetyl-S-(2-carboxypropyl)cysteine levels, proposed metabolic markers of this disorder, were documented in both siblings. Sequencing ECHS1 in 30 unrelated patients with paroxysmal dyskinesias revealed no further mutations.

CONCLUSIONS

The phenotype associated with ECHS1 mutations might be milder than reported earlier, compatible with prolonged survival, and also includes isolated paroxysmal exercise-induced dystonia. ECHS1 screening should be considered in patients with otherwise unexplained paroxysmal exercise-induced dystonia, in addition to those with Leigh and Leigh-like syndromes. Diet regimens and detoxifying agents represent potential therapeutic strategies. © 2016 International Parkinson and Movement Disorder Society.